In mobile wireless communication systems, wireless uplink resources from a mobile station to a base station are sometimes allocated based on SINR (signal-to-interface and noise ratio) of signals to be transmitted from the mobile station to the base station. At allocation, a scheduler of the base station acquires uplink SINR of a user, and allocates wireless resources to the user based on the acquired SINR.
When frequency scheduling is performed in OFDMA (orthogonal frequency division multiple access) systems, a scheduler of the base station uses the uplink SINR of each frequency block. A link and SINR from a mobile station to a base station are referred to as an uplink (UL) and uplink SINR, respectively. Further, the direction toward a mobile station from the base station is referred to as a downlink direction, and a link in a downlink direction is referred to as a downlink (DL).
For OFDMA systems adopting IEEE802.16e standards, one example of mobile wireless communication standards, there is no provision regarding a method of measuring uplink SINR (for example, refer to IEEE Std 802.16e-2005 and IEEE Std 802.16-2004/Cor 1-2005 (US)). Generally, SINR is measured using a unique signal or series of signals dedicated therefor. For example, a pilot subcarrier signal or a ranging signal is used, or a sounding signal is used (for example, refer to Japanese National Publication of International Patent Application No. 2004-523934 (paragraph number [0017])). Moreover, a method of determining the condition of a downlink propagation path by transmitting ACK/NACK information on a pilot signal to a base station from a mobile station in an OFDMA-TDD (time division duplex) system has conventionally been proposed (for example, refer to Japanese Laid-open Patent Publication No. 2005-244958 (paragraph numbers [0041] and [0043])).
FIG. 11 is a view for explaining a conventional uplink SINR measuring method. As depicted in FIG. 11, a transmission/reception frame 3 of OFDMA is constituted by a downlink subframe 4 and an uplink subframe 5. Conventionally, when the pilot subcarrier described above or the like is used as a signal for uplink SINR measurement, a base station 1 uses MAP information (UL-MAP) 6 of the downlink subframe 4 to notify a mobile station 2 of the wireless resources to be used for uplink SINR measurement such as timing and frequency blocks.
The mobile station 2, using the wireless resources indicated by the base station 1, transmits a signal for uplink SINR measurement to the base station 1. This signal for uplink SINR measurement is stored in a dedicated signal area 7 of the uplink subframe 5 to be transmitted. The base station 1 measures uplink SINR using the received signal for uplink SINR measurement. The base station 1 performs scheduling for uplinks based on a result of uplink SINR measurement and notifies the mobile station 2 using the uplink MAP information 6. The mobile station 2 transmits uplink data (UL data) to the base station 1 using accordingly the wireless resources indicated by the base station 1.
However, in the above methods using a pilot subcarrier, ranging signal, or sounding signal, because the base station, using a downlink, notifies a mobile station of wireless resources for uplink SINR measurement, and the mobile station transmits a signal for uplink SINR measurement to the base station using the wireless resources, there is a problem in that this strains uplink and downlink resources. Furthermore, when frequency scheduling is performed, the uplink SINR measurement is performed for each frequency block, and signals for uplink SINR measurement are required for the respective frequency blocks, further straining resources.